Magnetic resonance imaging using technique of positioning multi-slabs to be imaged

ABSTRACT

A magnetic resonance imaging system is provided for obtaining MR images by scanning a region of the object previously located on an object&#39;s positioning image. The system comprises a displaying unit, inputting unit, approximating unit, and locating unit. The displaying unit displays a plurality of tomographic images of the object as the positioning image, each of the tomographic images including an indication of a target of interest thereon. The inputting unit enables information about a running state of the target in a direction along the target to be supplied toward each of the tomographic images. The approximating unit calculates three-dimensionally an approximated curve indicating the running state of the target in the direction on the basis of the supplied information about the running state. The locating unit locates the region substantially perpendicular to the approximated curve.

RELATED APPLICATIONS

This is a division of co-pending, commonly assigned application Ser. No.11/330,114 filed Jan. 12, 2006 (now U.S. Pat. No. 7,953,468, issued May31, 2011), which was a division of Ser. No. 10/231,443 filed Aug. 30,2002 (now U.S. Pat. No. 7,190,992), which claim priority based onJapanese patent application Nos. 2002-10249 filed Jan. 18, 2002;2002-99508 filed Apr. 2, 2002, and 2002-101045 filed Apr. 3, 2002.

BACKGROUND

1. Technical Field

The present invention relates to magnetic resonance imaging for anobject and, in particular, to both of the magnetic resonance imagingwith a highly improved positioning technique for multi-slabs to belocated at the positions of object targets, such as a vertebral column,and an easy-to-use interface for the positioning technique.

2. Related Art

Magnetic resonance imaging (MRI) is generalized as a technique based onthe behavior of nuclear spins of an object positioned in a staticmagnetic field. A radio frequency (RF) signal of a Larmor frequency isapplied to the object in order to realize magnetic excitement of theobject. MR signals are induced and acquired responsively to theexcitement, and subjected to reconstruction processing of MR images ofthe object.

This magnetic resonance imaging is also suitable for imaging ofvertebral columns, such as a cervical vertebra, dorsal vertebra andlumbar vertebra. This is because the magnetic resonance imaging allowsan object's scanning section to be set at any angle and providescartilages and others with a higher contrast than that provided by otherimaging modalities. Normally, an imaging technique called a multi-slabscan is used for such vertebral columns, providing a plurality of MRimages of intervertebral disks.

For example, for diagnosing herniated disks using a magnetic resonanceimaging system, a section along the intervertebral disks is scannedbased on, normally, a multi-angle and multi-scan technique combined withthe multi-slab scan. For this imaging, it is required to plan a scan todetermine the positions of slices on a positioning image, which is forinstance a sagittal image of the intervertebral disks.

In normal diagnosis, a plurality of slices are located at one or moredesired disks in a mutually adjacent and parallel manner in order toexamine how deep the hernia develops in the column direction. Suchadjacent and parallel plural slices are called a slab. Hence, aplurality of slabs are located on the positioning image at arbitrarypositions and angles independently of each other. Hence, the slabs canbe located at different positions at different angles. The determinedslabs are then subjected to scanning carried out at a time based on themulti-angle and multi-scan technique.

How to plan an imaging scan, including how to locate slices, which issuitable for imaging the vertebral column of a human body (i.e., anobject) is exemplified by, for instance, Japanese Patent Laid-openPublication Nos. 1994-22933 and 1996-289888.

The former publication discloses, as one aspect, a technique of planninga scan for MR imaging. To be specific, with viewing a sagittal image ofa lumbar vertebra, an operator initially positions a slice in parallelwith a desired intervertebral disk on the image. Responsively to thispositioning operation, a calculator operates according to a series ofpreviously stored procedures so that a single initial slice is placed ata position and an angle, as specified. The calculator automaticallyplaces one or more adjacent slices on an upper or lower side of theinitial slice.

Referring to FIG. 1, a more practical way of setting a plurality ofslabs according to the teaching from the above former publication, whichis carried out interactively with an operator, is as follows.

(1) At a predetermined default position on a sagittal image, a firstslice is displayed;

(2) a mouse is used to adjust the first slice in its position,thickness, length, angle, and others;

(3) the number of slices to be placed adjacently to in parallel with thefirst slice is given, thus producing plural slices, thus producing afirst slab SL1;

(4) like the above, a second slice is displayed at a desired disklocation;

(5) a mouse is used to adjust the second slice in its position,thickness, length, angle and others; and

(6) the number of slices to be placed adjacently to in parallel with thesecond slice is given, thus producing plural slices, thus producing asecond slab SL2.

Through these operations, as exemplified in FIG. 1, the first slab SL1consisting of three slices and the second slab SL2 consisting of twoslices are designated.

Meanwhile, of the foregoing publications, the latter discloses atechnique of planning imaging carried out by an X-ray tomographicradiographing apparatus. Such technique can also be performed by amagnetic resonance imaging system. Practically, an auxiliary image(X-ray spectroscopic image) acquired around a vertebral column is usedto recognize each intervertebral disk, and then specify a middleposition in a plane between intervertebral disks to determine a scanposition. Further, from the auxiliary image, a centerline that passesthrough the vertebral column is drawn to detect a scan angle as beingperpendicular to the centerline. The thus-detected scan position andscan angle are incorporated in the planning data.

Normally, the vertebral column in the human body is curvedthree-dimensionally, so that planes positioned in parallel with theintervertebral disks are directed in various ways, respectively. Theconventional scan plan techniques use a single two-dimensional image, asdescribed by the foregoing publications. Thus, it was very difficultthat each slice to be imaged was almost completely in accord with eachintervertebral disk.

When taking these conditions into account, to precisely determine thedirections of slices in parallel with individual intervertebral diskstilted three-dimensionally may result in a second technique of using aplurality of images to determine a scan position and a scan direction.The use of the plurality of two-dimensional images means that a scanplan is established on each of the images. A period of time required forthe planning is, therefore, made longer remarkably, thus making thetotal imaging time longer as well. Adopting the second technique is notpractical.

Even for the same vertebral column, degrees of diagnostic interest aredependent on individual intervertebral disks. It is desired that thenumber of slices assigned to each intervertebral disk be, therefore,freely changeable every intervertebral disk, according to an upper limitof the number of slices, which results from a pulse sequence to be used,and degrees of medical interest. However, it was difficult to accuratelychange the number of slices every intervertebral disk on eachtwo-dimensional image. In addition, using a plurality of two-dimensionalimages for changing the number of slices was also almost impossible whenconsidering a time limit.

Moreover, the foregoing technique for positioning slices (slabs) causesan inconvenience when an operator desires to change or adjust contentsof the parameters of the slabs that have been determined once. Suchcases happen when the number of slices incorporated in a slab is desiredto be changed or sizes (e.g., width and/or length) of a slice aredesired to be changed. If assuming that changes in the number of slicescomposing a slab is desired, the following operations will be carriedout interactively with an operator:

(1) a mouse is used to move a cursor to a desired slab on a positioningimage for selection thereof;

(2) the mouse is again used to move the cursor to a window in which thenumber of slices are inputted, the window being positioned outside thepositioning image, and to select the window; and

(3) a keyboard is used to input a desired numeric value for the numberof slices.

As understood from the above, it is required for an operator that boththe mouse and the keyboard be used to change values of any parameters ofslices (such as the number of slices, sizes of a slice, or others).Using both tools is thus very burdensome for the operator. In addition,whatever the operator wants to change parameters of a slice, theoperator should move the cursor between the positioning image and theparameter-changing window, thus amplifying the burdensome operations.

Differently from setting slices to be scanned, a further region tosuppress influence resulting from blood flow and others, called asaturation region, should frequently be determined on a positioningimage. If one or more saturation regions are determined, an RFsaturation pulse is previously applied to the saturation regions, sothat signals acquired from the regions are suppressed.

In cases where setting such saturation regions is desired, a saturationregion of an arbitrary angle and size is placed at a default position ona positioning image in the similar manner to that for slices. Then amouse is used to click part of the initial saturation region to moveand/or rotate it, thereby being adjusted into a final saturation regionof a suitable angle and size.

However, when the number of saturation regions increases, theoperational work becomes heavy in proportional to the number ofsaturation regions and a time required for the setting work is madelonger, reducing efficiency thereof.

SUMMARY

The present invention has attempted to break through the foregoingsituations. A first object of the present invention is to provide bothof a magnetic resonance imaging system and a magnetic resonance imagingmethod, which are able to have a planning function for imaging, whichallows imaging slices to be located at desired positions of an objectmore precisely and quickly, even if the object is three-dimensionallycurved, like a vertebral column such as a lumbar vertebra.

A second object of the present invention is to provide both of amagnetic resonance imaging system and a magnetic resonance imagingmethod, which are able to have a function of freely changing the numberof imaging slices every intervertebral disk, depending on degrees ofclinical interest, in addition to the foregoing first object.

A third object of the present invention is to provide an interfaceequipped with a magnetic resonance imaging system, which allows anoperator to smoothly change values of parameters, or conditions, ofslices with extremely lightened burdens imposed on an operator.

A fourth object of the present invention is to provide an interfaceequipped with a magnetic resonance imaging system, which allows anoperator to improve efficiency of setting saturation regions, if thenumber of saturation regions to be set on a positioning image isincreased.

As one aspect of the present invention, there is provided a magneticresonance imaging system for obtaining an MR image of an object byscanning a region of the object previously located on a positioningimage previously acquired from the object. The system comprises adisplaying unit, inputting unit, approximating unit, and locating unit.The displaying unit displays a plurality of tomographic images of theobject as the positioning image, each of the tomographic imagesincluding an indication of a target of interest thereon. The inputtingunit enables information about a running state of the target in adirection along the target to be supplied toward each of the tomographicimages. The approximating unit calculates three-dimensionally anapproximated curve indicating the running state of the target in thedirection on the basis of the supplied information about the runningstate, and the locating unit locates the region substantiallyperpendicular to the approximated curve. The gist of this configurationis also adapted to a magnetic resonance imaging method as included inthe present invention.

Accordingly, even if a target (e.g., lumbar vertebra) to be diagnosed iscurved three-dimensionally within an object, the locating unit locates ascanning region (e.g., a plurality of slabs each consisting of one ormore slices) perpendicularly to the target in the running directionthereof in a more precise and speedy manner. In addition, depending ondegrees of medical interest, the scanning regions can be freely changedor increased in number.

By way of example, the tomographic images serving as the positioningimage is two in number and the region is one or more slabs eachconsisting of one or more slices. Preferably, the two tomographic images(for example, sagittal and coronal images of a vertebral column such asa lumbar vertebra) are substantially perpendicular to each other.

It is preferred that the inputting unit is configured to allow anoperator to specify a plurality of desired points, which indicates therunning state information, along the target on one of the twotopographic images. In that case, the approximating unit projects thedesired points specified on the one tomographic image onto the remainingtomographic image, and allows the operator to move the projected pointson the remaining tomographic image. The approximating unit furthercalculates an approximated curve passing three-dimensional crossedpoints at which the points on each of the two tomographic images arecrossed with each other. The locating unit allows the operator to selecta desired position along the approximated curve, and locates the slab atthe desired position of the approximated curve so that the slab issubstantially perpendicular to the approximated curve.

Still preferably, the locating unit allows the operator to specify thenumber of slices composing each of the slabs. In this case, the slabincluding slices of which number is specified is set.

A second aspect of the present invention is concerned with a magneticresonance imaging system, in which an MR image of an object is obtainedby scanning a region of an object previously is located on a positioningimage previously acquired from the object. The system, as an interface,comprises a displaying unit, inputting unit, and locating unit. Thedisplaying unit displays the positioning image, and the inputting unitinteractively allows two points to be located at desired points on thepositioning image. The locating unit locates the region substantiallyperpendicular to the positioning image on the basis of the located twopoints. The gist of this configuration is also adapted to a magneticresonance imaging method as included in the present invention.

Accordingly, it is enough for an operator to place two points at desiredlocations on a positioning image. This location of the two points willautomatically lead to the location of a scanning region, thus shorteninga period of time necessary for planning a scan and improving anefficiency of operations for the planning.

For instance, the region is a slab consisting of one or more slices tobe scanned for the MR image or a saturation region to be saturated in anMR signal. Preferably, by the inputting unit is configured torepetitively allow each set of the two points to be located at desiredpoints on the positioning image.

A third aspect of the present invention is also directed to an interfacefunction of a magnetic resonance imaging system for obtaining an MRimage of an object by scanning a region of the object previously locatedon a positioning image previously acquired from the object. The systemcomprises a displaying unit, setting unit, and changing unit. Thedisplaying unit displays a screen including a first window to allowconditions of the region to be given thereto and a second window inwhich the positioning image is displayed, an icon to which, at least,part of the region parameters being assigned being located in the secondwindow. The setting unit interactively allows the region to be set at adesired position on the positioning image, the region beingsubstantially perpendicular to the positioning image. The changing unitinteractively allows the slab to be changed on the basis of the regionparameters assigned to the icon. The gist of this configuration is alsoadapted to a magnetic resonance imaging method as included in thepresent invention.

Because the icon, to which, at least, part of the region parameters(e.g., slice parameters) are assigned is located together with thepositioning image in the same second window, operations needed forspecifying various parameters that define the region (e.g., multi-slabseach consisting of one or more slices) become smooth and efficient.

For example, the region is one or more slabs each consisting of one ormore slices and the region parameters assigned to the icon includes atleast one of the number of slices composing each slab, a thickness ofeach slice, and a length of each slice. Preferably, the icon is movablein the second window in response to an operator's command.

It is preferred that the changing unit interactively allows each slab tobe changed on the basis of the region parameters assigned to the icon.Preferably, the changing unit includes a mouse to be operated and isconfigured to select one of the region parameters assigned to the iconby clicking the icon with the mouse and to change each slab in one ormore of the region parameters by moving in a predetermine direction.

Still preferred is that, by the changing unit, in cases where theselected positioning condition on the icon is the number of slices, themouse is moved to show movements in an up-and-down direction on thescreen. When the selected positioning condition on the icon is the slicelength, the mouse is moved to show movements in a lateral direction onthe screen. Further, when the selected positioning condition on the iconis the slice thickness, the mouse is moved to show movements in anup-and-down direction on the screen.

It is also preferred that the magnetic resonance imaging system furthercomprises a switching unit configured to switch over functions of agiven button of the mouse responsively to a selection of one of theregion parameters on the icon.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 illustrates a conventional technique of locating slabs;

FIG. 2 is the functional block diagram showing an outlined configurationof a magnetic resonance imaging system according to various embodimentsof the present invention;

FIG. 3 shows a flowchart for planning a scan, which is carried out by amagnetic resonance imaging system according to a first embodiment of thepresent invention;

FIGS. 4A and 4B illustrate sagittal and coronal images of a lumbarvertebra employed by the first embodiment;

FIGS. 5A and 5B explain locating operations performed in the firstembodiment;

FIG. 6 explains locating operations performed in the first embodiment;

FIGS. 7A and 7B show approximated curves with wire frames on thesagittal and coronal images, which explain locating operations performedin the first embodiment;

FIG. 8 exemplifies a slab consisting of plural slices, which is locatedin the first embodiment;

FIG. 9 is a flowchart outlining for planning a scan, which is carriedout by a magnetic resonance imaging system according to a secondembodiment of the present invention;

FIG. 10 pictorially shows the screen of a display in the secondembodiment;

FIG. 11 outlines a flowchart for locating multi-slabs on a positioningimage;

FIGS. 12A and 12B show procedures for locating slabs by inputting eachpair of two points;

FIGS. 13A and 13B show procedures for locating slabs by inputting eachpair of two points;

FIG. 14 outlines procedures for changing (adjusting) amounts of sliceparameters of located slabs;

FIG. 15 shows procedures for adjusting slabs with use of an icondisplayed on the positioning image;

FIG. 16 shows procedures for adjusting slabs with use of an icondisplayed on the positioning image;

FIG. 17 explains a circulation of functions assigned to a certain buttonof the mouse;

FIG. 18 shows procedures for adjusting slabs with use of an icondisplayed on the positioning image;

FIG. 19 shows procedures for adjusting slabs with use of an icondisplayed on the positioning image;

FIG. 20 shows procedures for adjusting slabs with use of an icondisplayed on the positioning image;

FIG. 21 is a flowchart outlining for planning a scan, which is carriedout by a magnetic resonance imaging system according to a thirdembodiment of the present invention;

FIG. 22 outlines a flowchart for locating saturation regions on apositioning image; and

FIGS. 23A to 23C show procedures for locating saturation regions byinputting each pair of two points on a positioning image.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the accompanying drawings, preferred embodiments of thepresent invention will now be described.

First Embodiment

Referring to FIGS. 2 to 14, a first embodiment of the present inventionwill now be described.

FIG. 2 shows an outlined configuration of a magnetic resonance imaging(MRI) system in accordance with the embodiments of the presentinvention.

The magnetic resonance imaging system comprises a patient couch on whicha patient P as an object to be imaged lies down, static-field generatingpart for generating a static magnetic field, magnetic-gradientgenerating part for appending positional information to a staticmagnetic field, transmitting/receiving part for transmitting andreceiving radio-frequency (RF) signals, controlling/calculating partresponsible for the control of the whole system and for imagereconstruction, electrocardiographing part for acquiring an ECG signalserving as a signal indicative of cardiac phases of the object P, andbreath-hold instructing part for instructing the object to perform atemporary breath hold.

The static-field generating part includes a magnet 1 that is of, forexample, a superconducting type, and a static power supply 2 forsupplying a current to the magnet 1, and generates a static magneticfield H₀ in an axial direction (Z-axis direction) within a cylindricalbore (serving as a diagnostic space) into which the object P is insertedfor imaging. The magnet 1 includes shim coils 14. A current used tohomogenize a static magnetic field is supplied from a shim coil powersupply 15 to the shim coils 14 under the control of a host computer tobe described later. The couch top of the patient couch on which theobject P lies down can be inserted into the bore of the magnet 1 so thatthe couch top is withdrawn retractably.

The magnetic-gradient generating part includes a gradient coil unit 3incorporated in the magnet 1. The gradient coil unit 3 has three pairs(kinds) of x-, y-, and z-coils 3 x to 3 z used to generate magneticfield gradients that change in strength in the X-axis, Y-axis, andZ-axis directions, that is, the mutually-orthogonal physical-axisdirections of the gantry. The magnetic-gradient generating unit furtherincludes a gradient power supply 4 for supplying currents to the x-, y-,and z-coils 3 x to 3 z. The gradient power supply 4 supplies the x-, y-,and z-coils 3 x to 3 z with pulsed currents used to generate magneticgradients, under the control of a sequencer, which will be describedlater.

The pulsed currents supplied from the gradient power supply 4 to the x-,y-, and z-coils 3 x to 3 z are controlled, whereby magnetic gradientsthat can be changed in strength in the three physical-axis directions(that is, the X-, Y-, and Z-directions) are mutually synthesized. Thissynthesis produces a slice magnetic gradient G_(S) applied in a slicedirection, a phase-encode magnetic gradient G_(R) applied in aphase-encode direction, and a readout (frequency-encode) magneticgradient G_(R) applied in a readout direction, so that the gradientsG_(S), G_(E) and G_(R) are selectively specified and arbitrarily changedin strength. The slice, phase-encode, and readout directions arelogic-axis directions, which are also orthogonal to each other. Themagnetic gradients G_(S), G_(E) and G_(R) generated in the logic-axisdirections are superposed on the static magnetic field H₀.

The transmitting/receiving part includes a radio-frequency (RF) coil 7located in the vicinity of the object P in the diagnostic space insidethe magnet 1, and a transmitter 8T and a receiver 8R both connected tothe coil 7. Both of the transmitter 8T and the receiver 8R operate underthe control of a sequencer 5 described later. The transmitter 8Tsupplies the RF coil 7 with an RF current pulse at a Larmor frequency,which will cause a nuclear magnetic resonance (NMR). The receiver 8Rreceives MR signals (RF signals) via the RF coil 7, and then carries outvarious kinds of signal processing with the MR signals so that digitizedMR data (original data) are produced.

Furthermore, the controlling/calculating part includes a sequencer 5(also referred to as a sequence controller), host computer 6, calculator10, storage 11, display 12, input device 13, and voice generator 19.

Of these constituents, the host computer 6 operates on previouslymemorized software procedures, so that it has the functions of givingthe sequencer 5 pulse sequence information, managing the operations ofthe entire system, and performing an imaging plan, including apositioning plan, according to the present invention.

The sequencer 5, which has a CPU and various memories, is able to storepulse sequence information that has been supplied from the host computer6. Based on this pulse sequence information, the sequencer 5 controls aseries of operations to be performed by the gradient power supply 4,transmitter 8T, and receiver 8R. In parallel with this control, thesequencer 5 temporarily receives digital data produced from MR signalsthat the receiver 8R has created, and then transfers those data to thecalculator 10.

The pulse sequence information includes all information required foroperating the gradient power supply 4, transmitter 8T, and receiver 8Raccording to a desired pulse sequence. The pulse sequence informationthus includes the strength, duration, and application timing of pulsedcurrents that should be applied to the x-, y-, and z-coil 3 x to 3 z.

As the pulse sequence, a two-dimensional (2D) scan or athree-dimensional (3D) scan can be adopted. Pulse trains can preferablybe employed, if they include pulse trains based on an SE (spin echo)technique, an FE (field gradient echo) technique, an FSE (Fast SE)technique, a FASE (Fast Asymmetric SE) technique (also called a“half-Fourier FSE technique”), an EPI (echo planar imaging), and others.The FASE technique is realized based on a combination of the FSEtechnique and a half-Fourier technique.

The calculator 10 receives digital echo data sent from the receiver 8Rvia the sequencer 5, and maps those data in a Fourier space (also calleda k-space or frequency space) formed by an incorporated memory. Thecalculator 10 also performs a two-dimensional or a three-dimensionalFourier transform on the mapped data, so that an image in the real spaceis reconstructed. If necessary, synthesis processing of image data canalso be performed by the calculator 10. The calculation of the Fouriertransform may be assigned to the host computer 6, not always to thecalculator 10.

The storage 11 is able to memorize, in addition to echo data andreconstructed image data, image data that have experienced a widevariety of types of processing. The display 12 is formed to visualize animage. The input device 13 is used to provide the host computer 6 withvarious types of information including scan conditions, the type of adesired pulse sequence and its parameters, and desired one or more imageprocessing techniques. The input device 13 is provided with a mouse 13Mand a keyboard 13K.

The voice generator 19, which composes part of the breath-holdinstructing part, is configured to utter, for example, a voice messageinforming a patient (object) of the start or end of a breath hold inresponse to a command sent from the host computer 6.

Furthermore, the electrocardiographing part comprises an ECG sensor 17attached to the patient body to detect an electric ECG signal and an ECGunit 18 that performs various types of processing including thedigitization of the detected ECG signal and sends it to both thesequencer 5 and the host computer 6. Both of the host computer 6 and thesequencer 5 use this measured ECG signal as a timing signal during theperformance of an imaging scan on the basis of the EGG gating technique.

The entire operation of the above magnetic resonance imaging system willnow be described.

In the present embodiment, a lumbar vertebra is assigned to a region tobe imaged and subjected to MR imaging, in which imaging slices are setin parallel with desired intervertebral disks present in the lumbarvertebra and images of those slices are obtained. The imaging is carriedout based on a multi-slab scan technique.

Before this imaging, a scan plan, including a positioning plan forslices to be imaged, is conducted, which will be described below.

Practically, the host computer 6 cooperates with the storage 11, display12, and input device 13 to conduct the imaging plan in an interactivemanner together with an operator. The processing executed by the hostcomputer 6 during the scan plan will be outlined using FIG. 3.

Incidentally, the processing shown in FIG. 3 may be executed by thecalculator 10, not always limited to the configuration in which theprocessing is executed by the host computer 6. Another modifiedconfiguration is that the scan plan is executed by a planning apparatusnot only placed apart from the magnetic resonance imaging system butalso configured into a computer capable of communicating necessary dataand information with the magnetic resonance imaging system through thecommunication network.

Referring to FIG. 3, the processing executed by the host computer 6 willbe described. The host computer 6 determines whether or not images forpositioning slices to be imaged, or positioning images, should beacquired, while trying to detect a command from an operator, which isissued through the input device 13 (step S1). When the determinationshows that the operator desires the positioning images, the hostcomputer 6 instructs the sequencer 5 to scan both a sagittal slice and acoronal slice both including the lumbar vertebra of an object P with theuse of a specified pulse sequence (step S2). These scans produce asagittal image SG and a coronal image CO of the lumbar vertebra, asshown in FIGS. 4A and 4B. Those images are visualized on the same screenof the display 12 in for example a divided form.

There is a modification concerning with the positioning image. Thepositioning image, which can be adopted in the positioning according tothe present invention, is not limited to images of sagittal and coronalslices mutually crossed perpendicularly to each other. Two obliqueslices crossed at any angle other than 90 degrees may be used as long asthey contain a target to be imaged, such as the lumbar vertebra.

Then, the intervertebral disks HD of the lumbar vertebra visualized onone of the displayed sagittal and coronal images SG and CO, for example,on the coronal image, are subjected to designation of desired disks.Namely, the host computer 6 responds interactively to commands from theoperator to designate plural intervertebral disks HD to which imaging isdesired, by individually placing tiny rectangular ROIs (regions ofinterest) (hereafter, called points PT) on desired disks (steps S3 andS4). Setting the points PT is carried out such that both of the display12 and the input device 13 are used as a human-side interface tointeractively communicate necessary information with the operator viathe interface. More practically, the host computer 6 urges the operatorto place each point PT on a displayed image on the display 12.Responsively to this, the operator is to operate the input device 13 todesignate desired intervertebral disks HD in the vertebral column on thecoronal image CO by placing points PT at desired positions.

A modification concerning the above configuration is that, instead ofthe coronal image, the sagittal image may be adopted to make theoperator place points on the sagittal image.

The host computer 6 then calculates so that the positions of all thepoints PT on the coronal image CO are projected onto and displayed onthe sagittal image SG (step S5). Through this projection, the positionsof the points PT are projected only in the body-axis direction, so thatthe projected points PT are initially placed at predetermined positionsin the lateral direction on the sagittal image SG.

Then, responsively to instructions from the operator, the host computer6 operates to adjustably move the position of each points PT from theirinitial positions in the lateral direction on the sagittal image SG. Asa result of it, the position of each point PT can be positioned exactlyon each of the desired intervertebral disks HD (steps S6 and S7). On thecoronal and sagittal images on the display 12, points PT are displayedin a precise manner to be located on intervertebral disks HD to beimaged, as shown in FIGS. 5A and 5B.

After this setting operation, the host computer 6 calculates each ofvirtual points PT′ uniquely determined three-dimensionally by the pointsPT on each of the sagittal and coronal images SG and CO, at every pairof points corresponding to each other on both the images (refer to FIG.6; step S8).

For each of the coronal and sagittal images CO and SG, the host computer6 further calculates an approximated curve AC made of wire frames thatpass through all the virtual points PT′ (step S9). These approximatedcurves AC are obtained by, for example, approximated processing with theuse of splines (spline curves) or two-dimensional curve approximationsimply passing three points.

The approximated curves AC calculated based on wire frames are displayedin a superimposed manner on both the sagittal and coronal images SG andCO of the lumbar vertebra, for example, as shown in FIGS. 7A and 7B. Inplace of this display configuration, the approximated curve may be laidon only either image.

In cases where the operator who observed the displayed approximatedcurve AC desires that the setting operation should be re-performed, theprocessing of the host computer 6 will be returned to step S3 (stepS11).

At each point PT on the approximated curve AC, the host computer 6 thencalculates a plane, or flat surface, perpendicular to a tangent line ofthe approximated curve AC and memorizes information indicative of theposition of the plane (step S12). The thus-calculated plane becomes aslice to be imaged, if a given thickness is given to the perpendicularplane.

The reason why such planes perpendicular to the approximated lines ACbased on the wire frames can be used as slices to be imaged is follows.Although vertebral columns, such as a lumbar vertebra, are curvedthree-dimensionally, their curved lines are still continuous. It cantherefore be regarded that the directions of the intervertebral disksare also continuously changed. Hence an assumption that eachintervertebral disk is perpendicular to the approximated curve AC basedon the wire frames is allowed. If complying with this assumption, it isnatural to give up calculating the direction of each plane correspondingto each intervertebral disk. Therefore, instead, the wire frames thatpass through the intervertebral disks (i.e., approximated curve AC) canbe determined, and planes perpendicular to the tangent direction at eachpoint PT can be figured out as being the surfaces representativelydepicting intervertebral disks.

As described above, after the perpendicular plane has been determined atevery point PT, the host computer 6 operates to interactively control ofthe number of slices at each point PT (steps S13 to S17). Specifically,in reply to instructions issued from the operator, the host computer 6selects one of the plural points PT laid on the lumbar vertebra (stepS13). The host computer 6 then selects a desired number of slices to bescanned at the selected point PT, and displays the contours of one ormore slices corresponding to the selected number such that the slicesare placed adjacently to and in parallel with the already displayedperpendicular plane (step S14).

To be specific, the number of slices is selected, for example, byselecting a desired number from a pull-down menu displayed on the screenof the display 12. The number of slices, which can be selected by theoperator, ranges continuously from one to a plural number (for example,three).

The reason why a plurality of slices can be selected is based on thefollowing clinical two demands. One reason is that comparison betweensectional images of a corpus vertebra and an intervertebral disk, whichare acquired in the running direction of a vertebral column, iseffective for evaluating development of diseases such as a herniateddisk, so that it is extremely significant to plan scanning of bothsections of a corpus vertebrae and an intervertebral disk. The otherreason is that there is some need for diagnosing a region of a corpusvertebra CV as well as intervertebral disks.

FIG. 8 exemplifies a display state, in which the number of slices thathas been selected is two.

Returning to FIG. 3, the host computer 6 determines if or not the numberof slices that has been selected is two or more (step S15). If thisdetermination is YES (or, the number of slices is two or more), the hostcomputer 6 selects a slice to be placed at the currently handled pointPT (that is, the center of the currently handled intervertebral disk HD)in response to operator's instructions (step S16).

In the example of FIG. 8, according to the forgoing reasons forselection of a plurality of slices, one slice, or the upper slice SL1 inthe drawing is selected from the two slices SL1 and SL2, and located atthe point PT. In the location of the two slices SL1 and SL2 shown inFIG. 8, the lower slice SL2 is significant for diagnosis of atomographic image acquired from a one-side position, which is nearer tothe intervertebral disk, of the upper corpus vertebra CV2. Like theabove example, three slices can be placed. A further modification isthat a plurality of slices can be placed with a gap therebetween orgapless.

The foregoing selection of the number of slices and display processingis repeated at each point PT (step S17). Hence, as to eachintervertebral disk for which a scan is desired, a desired number ofslices, which is selected from a range of given numbers, are located inparallel with each other.

After the location of slices, the host computer 6 operates to receivevarious other scan conditions required for a multi-slab scan, which arepreviously set as default values and/or issued responsively tooperator's operations (step S18), thus completing the scanning plan.

The host computer 6 then instructs the sequencer 5 to perform themulti-slab scan, thereby providing MR images of the planned slices (stepS19).

Accordingly, the magnetic resonance imaging system according to thepresent invention is able to provide the scan planning function thatallows imaging slices to be located at desired positions, such asintervertebral disks, in a more precise and quicker manner, even if atarget to be scanned including vertebral columns, such as a lumbarvertebra, is curved three-dimensionally.

The scan plan used by the above embodiment requires a plurality oftomographic images (two images in the example of the embodiment), butthe use of such images is limited to the designation of intervertebraldisks to be targeted. Unlike the foregoing conventional technique thatuses a plurality of tomographic images to specify a scan position and ascan angle on each of the images, a time necessary for planning a scancan be shortened greatly. Hence a total imaging time is also shorteneddown to a practical level in medical care facilities.

Additionally, depending on degrees of medical interest and/or demandsfor comparison between cross sections of a corpus vertebra and anintervertebral disk, an operator is able to positionally change slicesto be scanned at every intervertebral disk. This enables the operator tolocate regions to be scanned, more steadily. Further, re-scanning can bealmost avoided, thus improving a patient throughput and alleviatingoperational work imposed on operators.

The present invention is not limited to the configurations describedabove, and there are various modifications that can still be applied tothe present invention. For example, a first modification relates toplacing points at intervertebral disks. In the foregoing embodiment,points placed on one image (e.g., coronal image CO) are projected ontothe other image (e.g., sagittal image SG) in the body-axis direction.Alternatively, an operator is able to place points at desired positionson both the images in an interactive way through the processing shown insteps S3 and S4 of FIG. 3. Moreover, in cases where a desiredintervertebral disk to be observed exists at only one place, it is alsopreferred that points are automatically located, in addition to theintervertebral disk itself, on the upper and lower sides thereof in adirection orthogonal with the longitudinal direction of the disk. Thatis, the total of three slices are automatically placed over theintervertebral disk desired, thus simplifying the operations necessaryfor scan planning.

Second Embodiment

Referring to FIGS. 9 to 20, a second embodiment of the present inventionwill now be described.

A magnetic resonance imaging system employed in the second embodimenthas the same configuration as that of the first embodiment (refer toFIG. 2), but has a different interface for planning a scan. Theinterface is functionally configured by the host computer 6, storage 11,display 12, and input device 13 (refer to a reference IF in FIG. 2).

A flowchart shown in FIG. 9 outlines the processing of a scan planinteractively carried out between the interface and an operator. Thisprocessing includes processes for acquisition and display of apositioning image (steps S21 and S22), processes for locating one ormore slabs each consisting of one or more slices (steps S23 and S24),processes for changing dimensions of the slices that have beendesignated once (steps S25 and S26), and processes for performing animaging scan (steps S27 and S28). These processes will be explained indetail by turns.

(A: Scanning Positioning Image)

In response to an operator's start command issued through the inputdevice 13, the host computer 6 operates to cause the sequencer 5 toperform a predetermined pulse sequence for a preparatory scan (step S21in FIG. 9). The performance of the pulse sequence produces MR signalsacquired by scanning a sagittal section along a region of a vertebralcolumn of an object P. Thus, from the acquired MR signals, thecalculator 10 reconstructs a sagittal image. The data of the sagittalimage is then memorized by the storage 11, while the sagittal image isdisplayed on the display 12 as a positioning image, as shown in FIG. 10(step S22 in FIG. 9). Using this positioning image, one or more slicescrossing the positioning image (i.e., sagittal image SG) are designatedas slices to be scanned by the imaging scan and their slices are changedin position or angle, if necessary,

After the scanning, a screen shown in FIG. 10 is provided on the display12. The screen includes windows 21 to 23. In a lower right area of thescreen, there is provided the display window 23 in which the sagittalimage SG serving as the positioning image is present. In a central areaof the sagittal image SG, the vertebral column of the object P isdepicted. On the sagittal image SG, an icon 24 for setting/changingslice parameters is laid, which will be later described.

In the upper right area of the screen, the window 22 is present, inwhich various kinds of sub-windows for specifying slice parameters (thenumber of slices, slice thickness, slice length and others) are placed.

In the left area of the screen, the window 21 is present, in whichdisplayed are sub-windows to be clicked to move (rotate, enlarge,contract, or the like) the image SG displayed in the window 23 and/orbuttons to be clicked to switch over setting modes.

(B: Locating Slices)

Locating slices (steps S23 and S24 in FIG. 9) follows the acquisitionand display of the sagittal image. This location is realized in aninteractive manner between the interface and an operator. During thelocation of slices and later-described changes (or adjustments) ofdimensions of the slices in their positions and angles, the patient P iskept being laid on the patient couch, with no gradient and RF pulseapplied.

Practically, a plurality of slices that compose one or more slabs, whichare subjected to the imaging scan carried out after the scan plan, arelocated based on the procedures shown in FIG. 11, which are executed bythe host computer 6.

The sagittal image SG that has already been described is used for thislocation of slices. First, at step S31, an operator inputs, to theinterface, amounts of desired slice parameters that include a slicethickness, slice length, the number of slices, and others applied to theimaging scan carried out later. Practically, the operator uses thekeyboard 13K to input numerical values into given frames 26 placed inthe window shown by the window 22 or uses the mouse 13M to move bars 25to desired scales in the window.

Then, in response to an operator's command, the host computer 6 operatesto place a first point for a first slab on the sagittal image SG (stepS32). Specifically, the operator uses the mouse 13M on the input device13 clicks a point 32, or the first point, on the sagittal image SG, asshown in FIG. 12A.

On specifying the point 32, the host computer 6 works so as toautomatically represent both of a dotted line DT and a cursor (i.e.,pointer) 31 along an initial direction and at an initial position on thesagittal image SG. The cursor 31, which is movable by the mouse 13M,connects the point 32 and the tip of the cursor 31.

Then, the tip of the cursor 31 is moved to a desired position, theoperator operates the mouse 13M to click at the desired position, or asecond point for the first slab, on the sagittal image SG (step S33). Inreplay to the operator's click, the host computer 6 will automaticallylocate and display a plurality of slices 34 between both the points 32and 33, as illustrated in FIG. 12B (step S34).

To be specific, using, as a center line CT, a straight line mutuallyconnecting both the points 32 and 33, a slice region that consists ofplural slices 34 according to the preset slice parameters (including thenumber of slices, slice thickness, and slice length) is placedsymmetrically to the center line. In this location, in a direction alongthe center line CT, the center of the slicing region (plural slices 34)is placed at the center of center line CT. As a result, a first slab 34Scomposed of plural slices 34 is designated at a desired area on thesagittal image SG. Each slice is set to the same thickness and length.

Incidentally, in the above procedure, each set of two points 32 and 33may be placed at any points on the sagittal image SG. Particularly, oneadvantageous way is to locate the two points 32 and 33 at both ends ofdesired intervertebral disks, as shown in FIG. 12B. This way isrelatively helpful for making slices, or slabs, locate as parallel aspossible with each disk.

In addition, it is also preferable that the length direction of slicesto be displayed on the sagittal image SG is assigned to a phase encodingdirection PE in performing an imaging scan for acquiring echoes for MRimages, as shown in FIG. 12B. Setting the phase encoding direction likethis is effective for reducing an aliasing noise on MR images.

Like the foregoing procedures in steps S32 to S34, a first point 35 fora second slab is placed (step S35), as illustrated in FIG. 13A, in whicha cursor 36 connected with the first point 35 through a dotted line DT.Then, as shown in FIG. 13B, a second point 37 for the second slab isplaced by the operator in the same manner as the above (step S36). Inreplay to this operation, the host computer 6 will automatically locateand display a plurality of slices 38 between both the points 35 and 37,as illustrated in FIG. 13B (step S37). As a result, a second slab 38Scomposed of plural slices 38 is designated at another desired area onthe sagittal image SG.

The information indicative of positions and angles of the plural slabsthus placed is stored in the storage 11.

According to the present embodiment, both of the first and second slabs34S and 38S can be located using one set of slice parameters in common.Furthermore, in the present embodiment, the four points 32, 33, 35, and37, which are needed for locating the two slabs 34S and 38S can beplaced in sequence on the sagittal image, or the positioning image.

(C: Changing Dimensions of Slices)

After locating the slices that make up of plural slabs, the hostcomputer 6 proceeds to step S25 to determine whether or not it isrequired to change the conditions of slices in an interactive mannerwith the operator. If the determination of YES (that is, it is requiredto change amounts of the slice parameters entirely or partly), theprocessing is moved to step S26, the detailed procedures of which areshown in FIG. 14. Images presented in the display window 23 in reply tothe procedures are exemplified in FIGS. 15, 16, and 18-20.

In the following, of the conditions of slices, the number of slices ischosen as a slice parameter to be changed, and changing “the number ofslices” after it was once set will be exemplified in detail.

First, at step S26A of FIG. 14, the host computer 6 operates to select aslab to be changed in the number of slices in an interactive manner withthe operator. In detail, as shown in FIG. 15, the mouse 13M is used tomove the cursor 31 to a change-desired slab, and is clicked, thus theslab being selected.

Then at step S26B, the host computer 6 selects a slice parameter usinginstructions from the operator. This selection is to decide which one ofthe plural slice parameters (i.e., slice thickness, slice length, thenumber of slices, and others) should be subjected to changes in amounts.As a practical way, as shown in FIG. 16, the host computer 6 moves thecursor 31 to the icon 24 for setting conditions, before acceptingseveral times of clicks of a right button R of the mouse 13M (i.e.,right clicks; refer to FIG. 17). Responsively to those clicks, the icon24 is able to change its functions 241 to 244 with the help of the hostcomputer 6 in a circulatory order illustrated in FIG. 17.

One function 241 is used for changing the thickness of a slice, anotherfunction 242 is used for changing the length of a slice, and anotherfunction 243 is used for simultaneously changing both of the thicknessand length of a slice. The remaining function 244 is directed tochanging the number of slices.

The host computer 6 receives a signal indicative of which function touse from the icon 24 and the mouse 13M. Depending on a function that hasbeen chosen, the host computer 6 will switch over left-button (L)functions of the mouse 13M. Changing amounts (value, distance, andothers) of a designated slice parameter (in the present embodiment, thenumber of slices, a slice length, or a slice thickness) is assigned tothe left button L. Hence, the host computer 6 serves as a switching unitfor switching over the functions of the left button L of the mouse 13M.

When changing values of the number of slices is desired, the function244 of the icon 24 is used. Hence, the operator repeats click operationsuntil the function 244 appears on the icon 24.

Then, at step S26C, the host computer 6 operates to accept and set acorrected-amount slice parameter interactively with the operator on ascreen shown in FIG. 9. This operation is carried out such that theoperator moves the mouse 13M upward and downward with a left click ofthe mouse 13M kept. Specifically, with the cursor 31 on the icon 24, themouse 13M undergoes its left click, thereby the cursor 31 being fixedthereat. With the cursor 31 fixed on the icon 24, the operator moves themouse 13M upward and downward.

In response to upward and downward movements of the mouse 13M, the hostcomputer 6 operates to change the number of slices displayed on thewindow 23, in the present embodiment, if the mouse 13M is moved upward,the host computer 6 increases the number of displayed slices incompliance with its moved amount.

FIG. 18 shows an example, in which the mouse 13M has been moved upwardto increase the number of slices up to five from three slices shown inFIG. 16.

By contrast, when the mouse 13M is moved downward, the host computer 6detects a downward movement of the mouse 13M and decreases the number ofdisplayed slices in compliance with its moved amount.

In this increasing and decreasing case, as typically shown in FIG. 18,both of a slice thickness and a slice length that have been attainedbefore the changes are still maintained even after the changes. Theslices that are increased or decreased are always added to the originalslices so as to maintain an entirely symmetric slab form to thecenterline thereof. That is, when increasing slices, slices aresymmetrically added to both sides of the original ones, one by one, twoby two, three by three, or others. In contrast, when decreasing slices,slices are symmetrically reduced from both sides of the original ones,one by one, two by two, or others. During the above operations, the icon24 is kept at the same place on the window 23.

In the present embodiment, slice parameters to be changed in amounts isnot limited to the number of slices, but can be performed with changinga slice length and a slice thickness. FIG. 19 illustrates changes ofslice lengths, while FIG. 20 illustrates changes of slice thicknesses.

Changing slice lengths can be done after the selection of the function242 at the icon 24 on the window 23 (refer to FIG. 19). An operatoroperates the mouse 13M to move the cursor 31 on the icon 24, and clicksthe left button of the mouse 13M, during a period of the left clickoperation the mouse 13M is moved right and left. In response to such arightward or leftward movement of the mouse 13M, the host computer 6changes the lengths of the slices belonging to a desired slab, asillustrated by arrows in FIG. 19.

In the present embodiment, a rightward movement of the mouse 13M causesthe lengths of the slices to be lengthened, while a leftward movement ofthe mouse 13M causes the lengths thereof to be shortened. Lengthened orshortened amounts depend on moved distances of the mouse 13M. Changingslice lengths are reflected at a time into all the slices of a selectedslab.

Like the above, changing slice thicknesses can be done after theselection of the function 241 at the icon 24 on the window 23 (refer toFIG. 17). In the same procedures as those in changing slice lengths,moving the mouse 13M in the right and left directions makes it possiblethat slice thicknesses of all the slices included in the same desiredslab are changed, as pictorially shown in FIG. 20. Changing slicethicknesses can be performed dependently of changing the number ofslices.

As described above, the icon 24 that has been displayed on thepositioning image, such as a sagittal image, is used by an operator tochange desired one or more slice parameters (conditions).

Incidentally, the above icon 24 is not always used for only changingamounts of slice parameters, but can be used to initially set amounts ofslice parameters before the display of slabs on the display. Further,instead of using the icon 24, the window 22 can be used as well tochange amounts of slice parameters. The position of the icon 24 can bemoved to any position on the sagittal image through drag-and-dropoperations while a predetermined button on the keyboard 13K etc. ispushed.

(D: Imaging Scan)

After completion of setting the slice parameters, the host computer 6responds to an operator's command to start an imaging scan, thusinstructing the sequencer 5 to perform a predetermined pulse sequencefor the imaging scan. The sequencer 5 performs the pulse sequence, inwhich the strengths and timings of both of RF pulses and gradient pulsesare controlled to scan the slices of the slabs located based on theabove procedures B and C.

Images of the slices obtained by the imaging scan can selectively bedisplayed in the window 23 of the screen of the display 12 in responseto an operator's command. Doctors use the images to diagnose diseasessuch as herniated disk.

As configured and operated above, the interface according to the presentsecond embodiment provides various advantages.

First of all, only placing two points on the positioning image willautomatically lead to setting a slab. And continuously placing anotherset of two points on the positioning image will automatically lead tosetting another slab. It is, therefore, possible to continuously locateslabs, thus improving efficiency in locating slabs, compared to theconventional models, thus contributing a whole imaging time of anobject.

Second, the icon 24 as well as the window 23 for setting and changingamounts of slice parameters can be used, so that an operator is able tosmoothly (i.e., quickly and precisely) determine amounts of sliceparameters. Particularly, in cases where frequently used sliceparameters are used, using the icon 24 is very effective, because it isenough for the operator only to use the same mouse 13M, and it is notrequired to move the operator's hand between the mouse 13M and thekeyboard 13K. Thus, burdensome operations of touching both the mouse 13Mand the keyboard 13K, like the conventional models, are avoided.

Third, the icon 24 is displayable on a positioning image. Hence, it isenough that an operator watches only the same window 23, therebyproviding a smooth operation for setting slice parameters. Unlike theconventional models, it is not necessary to move a cursor between, ifexplained in FIG. 10, the positioning image SG (window 23) and thecondition-setting window 22.

Fourth, the icon 24 allows both the number of slices and slicethicknesses to be changed with the mouse 13M alone, thus beingsimplified in operations and being highly convenient. In theconventional models, to change the number of slices and slicethicknesses on a sagittal image involves the same movement directions onthe screen (refer to FIGS. 18 and 20), so that the operations werecomplicated and burdensome.

Fifth, setting and changing amounts of slice parameters using the iconcan be done slab by slab, being speedy in positioning slices and highlyconvenient.

Sixth, the icon 24 is highly functional, because the icon makes itpossible to selectively display one from a plurality of slice parametersand determine the amount of the selected slice parameter. In otherwords, compared to a situation where an icon is displayedcorrespondingly to a slice parameter in a one-by-one correspondence (forexample, an icon dedicated to setting only slice thicknesses and anothericon dedicated for setting the number of slices), the icon 24 accordingto the present embodiment has multiple functions. By way of example, asdescribed before, a plurality of slice parameters, such as slicethicknesses, slice lengths, and the number of slices, can be set andchanged with the use of the one icon 24.

The multi-functional icon promotes more effective use of thelimited-size screen on the display. Further, the icon 24 itself ismovable to any position on the positioning image, thereby providing aneasy-to-observe target image (such as an image of the lumbar vertebra)without being hidden by the icon.

According to the present embodiment, there are still various kinds ofmodifications.

A first modification is the configuration in which the icon 24 can beplaced outside the display window 23, not limited to the inside thereofin which the positioning image SG is present.

A second modification concerns the parameters of each slice which areadjustable. In the second embodiment, the icon 24 has been configured toset amounts of both its slice thickness and length. In addition to thosetwo parameters, the remaining dimension, or the length along the depthdirection in the figures, may be added so that it can be adjustable inthe foregoing changing process.

More significantly, the interface function according to the secondembodiment can be reduced into practice with the use of a conventionaltechnique for changing slices, without using the foregoing changingprocess described by the second embodiment.

Further, part of the interface function according to the secondembodiment can be practiced in a combined manner with the locatingtechnique described by the first embodiment. Precisely, a plurality ofslabs each consisting of one or more slices are three-dimensionallylocated based on the locating technique described by the firstembodiment, and then the slabs are adjusted in slice sizes and thenumber of slices based on the changing slice technique (C) described bythe second embodiment.

Third Embodiment

Referring to FIGS. 21 to 23, a third embodiment of the present inventionwill now be described.

A magnetic resonance imaging system employed by the third embodiment hasthe same configuration as that of the first embodiment (refer to FIG.2), but has a different interface for planning a scan. That is, theinterface is modified from the second embodiment in that one or moresaturation regions are located together with slices (composing slabs).The interface is functionally configured by the host computer 6, storage11, display 12 and input device 13.

A flowchart shown in FIG. 21 outlines the processing of a scan planinteractively carried out between the interface and an operator. Thisprocessing includes processes for acquisition and display of apositioning image (steps S41 and S42), processes for locating one ormore slabs each consisting of one or more slices (steps S43 and S44),processes for locating one or more saturation regions (steps S45 and46), and processes for performing an imaging scan (steps S47 and S48).

The processes for acquisition and display of a positioning image (stepsS41 and S42) are carried out in the similar way to those in the firstembodiment. Accordingly, the display 12 provides the display of aplanning image, which is similar to that in the second embodiment (referto FIG. 10), but different from that in that there is no icon 24 thathas shown in FIG. 10.

The processes for locating one or more slabs (steps S43 and S44) arethen carried out in the same way as that in the second embodiment.

The processes for locating one or more saturation regions (steps S45 and46) are then carried out as follows. This locating processing can bedone after the location of slabs, as in this embodiment, or before thelocation of slabs. If there is no necessity of using saturation regions,the present locating processes can be omitted from the interfacefunction. Still, by way of example, pressing a preset button in theregion 21 shown in FIG. 10 makes it possible to change, at any time, themode for locating slices to another mode for locating saturationregions.

Practically, the host computer 6 executes the location of saturationregions in an interactive way with an operator according to theprocessing shown in FIG. 22.

The sagittal image (positioning image) SG of a lumbar vertebra is stillpresent in the display window 23, as it is after having been subjectedto the location of slabs. This sagittal image SG is continuously usedfor locating saturation regions.

With the sagittal image SG displayed, saturation conditions are given byan operator as practical values or amounts (step S51). The saturationconditions include a desired width of a saturation region.

In response to an operator's command, the host computer 6 places a firstpoint 62 for a first saturation region at a desired position on thesagittal image SG, as shown in FIG. 23A (step S52), like the location ofthe first slab described in the second embodiment.

Responsively to another operator's command, the host computer 6 operatesto place a second point 64 for the first saturation region at anotherdesired position (step S53; refer to FIG. 23B). For placing the secondpoint 64, an automatically visualized pointer 63 and a dotted line DTconnecting the tip of the pointer 63 to the first point 62 is helpful(refer to FIG. 23A).

After placing both the points 62 and 64, the host computer 6 places onthe sagittal image SG a first saturation region 65 having apredetermined width according to the given saturation condition (stepS54). In detail, the saturation region 65 is formed into a rectangularshape symmetry to a centerline connecting both the points 62 and 64.

In the same way as the above, a second saturation region 66 is locatedby specifying another set of two points through the processes at stepsS55 to S57 (refer to FIG. 23C).

When the above preparation is completed, an imaging scan using a desiredpulse sequence is carried out to produce MR images at the designatedslices. During the scanning, the designated one or more saturationregions undergo previous application of RF saturation pulses. Hencemagnetic spins that are present in the saturation regions are previouslyflopped, reducing MR signals to be acquired by the imaging scan.

According to the third embodiment, only placing two points on thepositioning image will automatically lead to setting a saturationregion. And continuously placing another set of two points on thepositioning image will automatically lead to setting another saturationregion. It is therefore possible to continuously locate saturationregions, thus improving efficiency in locating saturation regions,compared to the conventional models, thus contributing a whole imagingtime of an object.

By the way, part of the interface functions according to the thirdembodiment can be practiced in a combined manner with the locatingtechnique described by the first embodiment. Precisely, a plurality ofslabs each consisting of one or more slices are three-dimensionallylocated based on the locating technique described by the firstembodiment, and then one or more saturation regions are located based onthe locating technique described by the third embodiment.

Although the embodiments described above contain many specificities,these should not be construed as limiting the scope of the presentinvention but as mealy providing illustrations of some of the presentlypreferred embodiments of the present invention. The person skilled inthe art can alter or modify the present invention into a variety ofdifferent modes without departing from the scope of the appended claimsand their equivalents.

For example, the present embodiment has been described about themagnetic resonance imaging system having the cylindrical-bore gantry,but any type of system can be adopted in the present invention, notlimited to the shape of the gantry and the applied direction of a staticmagnetic field. Such an example can be shown as a magnetic resonanceimaging system with an open type of gantry.

What is claimed is:
 1. A magnetic resonance imaging system for obtainingan MR image of an object by scanning a slab region of the object locatedon a positioning image previously acquired from the object, the systemcomprising: a display; an operator input circuit; and at least onecontrol computer circuit connected to the display and the operatorinput, circuit, the at least one control circuit configured to: causethe display to display a screen including a first window which providesscan conditions for at least one slab region of an object, a secondwindow in which a previously acquired positioning image is displayed,and an icon located in the second window, wherein at least one slabregion parameter is assigned to the icon; and provide for said slabregion to be set at a desired position on the positioning image,interactively via the operator input circuit, the slab region beingsubstantially perpendicular to the positioning image; while alsoproviding for the slab region to be dimensionally changed interactivelyby the operator input circuit on the basis of the at least one regionparameter assigned to the icon.
 2. The magnetic resonance imaging systemof claim 1, wherein the at least one slab region is at least two slabs,each consisting of one or more slices, and wherein the at least oneregion parameter assigned to the icon include at least one of (a) thenumber of slices composing each slab, (b) a thickness of each slice, and(c) a length of each slice.
 3. The magnetic resonance imaging system ofclaim 1, wherein the icon in the second window is movable in response toan operator command via said operator input circuit.
 4. The magneticresonance imaging system of claim 2, wherein the at least one controlcomputer circuit provides for each of the one or more slabs to beinteractively changed on the basis of the at least one region parameterassigned to the icon.
 5. The magnetic resonance imaging system of claim4, wherein the operator input circuit comprises a mouse to be operated,and wherein one of plural region parameters assigned to the icon isselected by clicking on the icon with a mouse controlled cursor and oneor more of the region parameters of each slab is changed by moving themouse in a predetermined direction.
 6. The magnetic resonance imagingsystem of claim 5, wherein, in cases where the selected region parameteron the icon is the number of slices, movements in an up-and-downdirection on the screen are effected by mouse movements; in cases wherethe selected region parameter on the icon is the slice length, movementsin a lateral direction on the screen are effected by mouse movements;and in cases where the selected region parameter on the icon is theslice thickness, movements in an up-and-down direction on the screen areeffected by mouse movements.
 7. The magnetic resonance imaging system ofclaim 6, wherein switch over functions of a given button of the mouseare effected in response to a selection of a region parameter on theicon.
 8. The magnetic resonance imaging system of claim 1, wherein, inresponse to two points being interactively located at desired points onthe positioning image, the slab region substantially perpendicular tothe positioning image is located.
 9. A method of planning a slab regionto be scanned by magnetic resonance imaging, the slab region of theobject being previously located on a positioning image previouslyacquired from the object, the method comprising: using at least onecontrol computer circuit to drive a display screen including a firstwindow which provides scan conditions for at least one slab region of anobject and a second window in which a previously acquired positioningimage is displayed, with an icon also being displayed in the secondwindow, at least one slab region parameter having been assigned to saidicon; using at least one operator input circuit connected to saidcontrol computer circuit to interactively set the slab region at adesired position on the positioning image, the slab region beingsubstantially perpendicular to the positioning image while alsointeractively changing the slab region on the basis of the at least oneslab region parameter assigned to the icon.
 10. An interface for amagnetic resonance imaging system in which a slab of an object to bescanned is located using a positioning image previously acquired fromthe object, the slab comprising one or more slices, the interfacecomprising: a display; a mouse having a button; and at least one controlcomputer circuit connected to the display and the mouse, the at leastone control computer circuit configured to: cause the display to displaya screen including a window in which the positioning image and an iconare displayed, wherein at least one region parameter for the slab isselectably assigned to the icon; according to input from the mouse,adjust switchably assigned region parameters, and switch differentfunctions of the button is response to a selection of a region parameteron the icon.
 11. The interface of claim 10, wherein the regionparameters include (a) the number of slices, (b) a slice length, and (c)a slice thickness, and wherein the functions switched between include:an increase/decrease in the number of slices to be displayed on thepositioning image in response to selecting the number of slices, anadjustment of a length of each slice to be displayed on the positioningimage in response to selecting the slice length, and an adjustment of athickness of each slice to be displayed on the positioning image inresponse to selecting into the slice thickness.